need help

Exhaust from a process is contaminated with 500ppm of benzene. The exhaust is passed through two parallel absorption beds filled with activated carbon at a rate of 2000m3/min at 30C and 1atm. Only one absorption bed is used at a time while the other is regenerated, and each is run for 3 hours before it is regenerated. Assuming that 99% of the benzene is captured in the absorption beds, how much activated carbon is in each bed? Benzene has a molecular weight of 78g/mol, and each gram of activated carbon absorbs 0.2grams of benzene